As a mulching sheet for agriculture, nonwoven fabrics are used. For example, a nonwoven fabric consisting of polyethylene fine fibers which are obtained with a flash-spinning process is used. The nonwoven fabric is sold as Tyvek, which is a trade name. Tyvek has very fine pores. Therefore, Tyvek is superior in waterproofing and shading. If Tyvek is spread on the ground, weeds are prevented from growing. Furthermore, if Tyvek is spread on the ground, it protects fertilizer from being washed away from the ground and also protects a root of a fruit tree from being damaged. As a mulching sheet other than nonwoven fabric, black films consisting of synthetic resins such as polyethylene or polyvinylidene chloride are used. The black films are also superior in waterproofing and shading.
However, it causes a problem to dispose synthetic films or nonwoven fabrics consisting of synthetic fibers such as polyethylene fine fibers. It causes an environmental problem because synthetic films or nonwoven fabrics are incinerated. Especially, the problem is serious when the mulching sheets are largely used.
Therefore, nonwoven fabrics consisting of biodegradable fibers instead of the nonwoven fabrics consisting of synthetic fibers are used as the mulching sheets. For example, following Patent reference 1 discloses the use of cellulose fibers instead of the synthetic fibers. If nonwoven fabric consisting of cellulose fibers which are biodegradable is used as the mulching sheet, it will decompose and disappear during its use or after the use. Therefore, it prevents destruction of the environment.
Patent reference 1: JP2005-198617
Patent reference 1 discloses combining non-dewaxed cellulose fibers with dewaxed cellulose fibers because they have the ability to waterproof nonwoven fabric consisting of cellulose fibers. However, it is expensive to add the dewaxing process to produce the dewaxed cellulose fibers. Furthermore, cellulose fibers must be closely and extensively accumulated to bring out the effects of waterproofing and shading. However, by doing so, the nonwoven fabric becomes difficult to biodegrade.